1. Field of Art
The present invention relates to a control apparatus that has wide applications to controls in iron and steel plants, and paper manufacturing plants, as well as for industrial systems, such as in the automobile industry, and public systems encompassing water supply and sewerage systems.
2. Description of Relevant Art
FIG. 1 shows configuration of a conventional control apparatus 100. In the control apparatus 100, a control program executing circuit 114 is adapted to process input data from a plurality of I/O (input/output) devices 200, which data are input via I/O interfaces 117 and a system bus 119 to input registers in a control data memory 116, where the input data are used for implementation of a control program stored in a control program memory 115 to be executed in the control program executing circuit 114, of which operation results are written to unshown output registers in the control data memory 116.
FIG. 2 shows associated data flows. For this, before the execution of operations of the control program, input data from input devices 200, as the whole, are input from the input devices 200 to the input registers 116a, and after the execution of operations of the control program, whole data stored in the output registers 116b are output to the I/O devices. This process is referred to as a batch I/O.
Therefore, whole input data are input to the input registers 116a even if input data from the input devices 200 include no variations, and whole data stored in the output registers 116b are output to the I/O devices 200 even if output data include no variations.
The control apparatus 100 has for the I/O devices 200 a total number of I/O connections about 1000 even for systems of an intermediate scale, thus taking much time for the batch I/O, unsuccessfully achieving a shortened control period.
To this point, there has been disclosed a programmable controller (refer to e.g. Japanese Patent Publication No. 3317601) for data transfer along a batch I/O between I/O devices and I/O registers in a control apparatus, that includes, when executing a control program, monitoring operands of specific sequence instructions, and discriminating a state of execution of CPU, to set up flags of an instruction for data transfer on I/O registers needing data transfer, and when making data transfer between those I/O registers and I/O modules, executing data transfer to I/O modules with respect simply to I/O registers having data transfer instruction flags set thereon, allowing for a minimized data transfer rate, as necessary.
The above-mentioned programmable controller reads whole I/O registers to check status of their transfer instruction flags. This disables reduction of the time required for checks of transfer instruction flags on I/O registers needing no checks, as a problem.
Further, in the case of a read/write instruction for reading a control data from a control data memory and writing-back a result of an operation process executed thereon to the control data memory, the programmable controller writes the result to the control data memory unconditionally even if the result of operation is identical to the read control data. This operation prevents from achieving omission of unnecessary writing, as a problem.